There is a constant need for improved permanent magnet materials which are stronger, more permanent, lighter in weight, and less expensive. These needs have sharply increased with miniaturization of electrical and electronic devices, and it is now more than ever desirable to produce extremely powerful, small sized and light weight permanent magnets. The need exists in such diverse fields as airborne and spaceborne electronic equipment, where one of the more important illustrative needs is for more powerful, smaller, lighter, permanent magnets for traveling wave tubes and the like, and in commercial products such as special motors, gyros, switches, hearing aids and other extremely small electric devices such as electric watches and the like. For example, there does not now exist a satisfactory permanent magnet for a ladies-sized watch, available at a commercially competitive price.
There are various properties sought in today's permanent magnet materials, including for example, coercive force, residual induction, thermal stability, Curie temperature, mechanical hardness, and the like. Assuming that desirable characteristics can be achieved for the other necessary properties, a particularly valuable combination is high residual induction, together with high coercive force such that the combination of these properties, otherwise known as the energy product, is as high as possible.
In FIG. 1, there is illustrated a combination of remanence and coercive force for one material of the present invention, and for several prior art materials. Included in the FIGURE is a curve designated 11, illustrating the properties of platinum cobalt, a highly desirable magnetic material, a curve 12, which is representative of ferrite material and a curve 13 which is typical of the alnico class of magnets, these three being prior art materials. Curve 14 illustrates like properties for a presently preferred material according to this invention. Curve 15 illustrates the same properties for SmCo.sub.5 in the absence of Sm.sub.2 Co.sub.7, and in unsintered condition.
Prior to the present invention, platinum cobalt material was the quality standard in the permanent magnetic material art. It has a very high coercive force of about 4,000 oersteds, and a remanence of about 6,000 gauss, and an energy product of approximately 9 .times. 10.sup.6 gauss-oersteds. Where the need is for high performance, permanent magnetic materials justify the cost, as in the case of airborne and spaceborne equipment, platinum cobalt was indeed the material of choice, and it is the standard by which new promising materials should be measured in terms of absolute performance. The new magnets of the present invention, however, are so far superior that they now are the new standard of excellence.
Where the need is for a high quality, permanent magnet material available at a commercially realistic price, the ferrite materials have found substantial use and application. While significantly less satisfactory in performance than platinum cobalt, having energy products up to about 3.5 .times. 10.sup.6 gauss-oersteds, they are, nevertheless, realistically recognized as being high performance materials, and are available at prices which are a small fraction of the cost of platinum cobalt. Where high permeability together with low stability is tolerable, a material such as Alnico-9 (illustrated in curve 13) is a very satisfactory magnetic material.
Recently, it has been found that certain rare earth combinations with cobalt are effective magnets and in particular, yttrium-cobalt mixtures corresponding to the proportions YCO.sub.5 have a high theoretical potential, and practical yttrium-cobalt magnets have been produced with an actual energy product greater than 1 .times. 10.sup.6 gauss-oersteds but less than 5 .times. 10.sup.6 gauss-oersteds. Such magnets are disclosed for example, in Strnat U.S. Pat. No. 3,540,945.